Soot sheet characteristics of turbulent diffusion fire using equivalent ellipse method

This paper investigates the soot sheet characteristics of buoyant turbulent fires using laser-induced incandescence technique. Experiments are carried out for four fires using propane and nitrogen hybrid gases as fuel with propane fractions of 1.0-0.4. An equivalent ellipse method in previous literature was employed to evaluate soot sheet characteristics. The results show that soot sheet mainly exists in two kinds of morphology: one is small piece and the other is narrow and long piece. Both the probability density functions of the length and width of the equivalent ellipse and soot volume fraction of soot sheet are strongly dependent on height. In addition, the effect of propane fraction on the probability density functions is always opposite in the lower and middle part of the fires, while no obvious effect can be found in the upper part of the fires. Soot sheet number is found to increase with height except when propane fraction is 0.4. The total soot sheet number increases linearly with height within the scope of this paper.